Many catalytic processes are performed in reactors containing a series of separate catalytic beds. Reactors used in the chemical, petroleum refining, and other industries for passing liquids or mixed-phase liquid/gas mixtures over packed beds of particulate solids are employed for a variety of different processes. Examples of such processes include: catalytic dewaxing, hydrotreating, hydrodesulphurization, hydrofinishing, and hydrocracking. In these processes a liquid phase is typically mixed with a gas or vapor phase and the mixture passed over a particulate catalyst in a packed bed within a downflow reactor.
In downflow reactors, it is necessary that the gas and liquid are properly mixed and uniformly distributed across the horizontal cross section of the reactor prior to contacting each catalyst bed. Such uniform distribution of the gas and liquid provides major advantages, including: efficient utilization of catalyst, reduced catalyst top layer attrition, improved yields, improved product quality, and increased run lengths. Generally in a downflow catalytic reactor, a plurality of catalyst beds are arranged within the reactor, and a distributor system for the efficient mixing of gas and liquids is disposed above each catalyst bed. The region between catalyst beds is normally provided with a gas injection line to provide additional gas to compensate for gas consumed in the previous catalyst bed. The injected gas can also act as a quench gas for cooling the feed exiting a catalyst bed prior to the feed entering the next catalyst bed. Generally, the injected gas is hydrogen or comprises hydrogen. The liquid feed falling from the above-lying catalyst bed is allowed to accumulate on a collection tray. The quench gas and liquid then pass into a mixing chamber where a swirling movement of the liquid is provided. This enables good mixing of the liquid and thereby provides even temperature conditions of the liquid. Gas-liquid mixing also takes place inside the mixing chamber.
The fluid from the mixing chamber flows downward onto a deflector or impingement plate, whereby the flow is redirected onto a distributor tray having a large number of downflow openings for the passage of liquid. For cross-sectional liquid flow distribution, the downflow openings of conventional apparatus can comprise one or more conduits, or chimneys. The chimney is a cylindrical structure with an open top and one or more openings in the upper portion of its height through which a gas phase can enter. The gas phase travels downward through the length of the chimney. The lower portion of the chimney can have one or more lateral openings for liquid flow through which a liquid phase can enter the chimney and contact the gas phase. As liquid continues to accumulate on the distributor tray, the liquid will rise to a level that covers the lateral opening(s) in the chimney so that the passage of gas is precluded and so that the liquid can enter through the lateral opening(s) into the chimney. Gases and liquids egress via an opening in the bottom of the chimney, through the distributor tray, and onto an underlying catalyst bed. A disadvantage of conventional conduits or chimneys is that, due to the low turbulence around liquid streams, only limited mixing between the two phases will occur.
A good flow distribution device for a catalytic reactor should meet the following four basic requirements: provide even distribution of feed to a catalyst bed over a range of gas and liquid feed rates; be tolerant to certain out-of-levelness of the distribution tray; provide good gas-liquid mixing and heat exchange, and require minimum catalyst bed height to fully wet the underlying catalyst bed. Because conventional chimneys rely on the static liquid height on the tray as the driving force for liquid flow into the chimney, they are deficient in meeting these criteria due to poor tolerance for deviations from levelness of the distributor tray, as well as exhibiting suboptimal spray discharge of fluids onto the underlying catalyst bed, and other deficiencies.
One of the key considerations in flow distributor design is the discharge pattern of liquid and gas from the device. A conventional chimney distributor provides a limited number of points of contact of the liquid feed with the catalyst bed. As a result, a larger distance from the chimney to the bed is required to wet the catalyst surface.
U.S. Pat. No. 7,473,405 to Kemoun et al. discloses a nozzle device for coupling with a fluid distribution conduit.
There is a continuing need for hydroprocessing reactor apparatus providing improved hydrogen/oil mixing at the mixing tray, more uniform and consistent liquid distribution on the catalyst bed, a decreased mixing tray height, and decreased amounts of fabrication material, as well as easier maintenance, assembly and disassembly. There is also a need for systems and apparatus that provide improved tolerance for distributor tray out-of-levelness conditions. There is still a further need for fluid distribution apparatus that can provide more uniform distribution of liquid on a catalyst bed under liquid-only conditions.